Polyurethanes (PU) are prepared from polyols and isocyanates. The Polyurethanes Book, Randall, D., Lee, S., John Wiley & Sons, New York, 2003. Uhlig, K., Discovering Polyuretanes, Hanser Gardner: New York, 1999. The isocyanate groups react with the hydroxyl groups on the polyol to form of urethane bond. In general, the polyol can be a low molecular weight polyether or polyester. The isocyanate can be aliphatic or aromatic and in the preparation of linear PUs is typically di-functional. However, isocyanates with greater functionality are used in preparing thermoset PUs. The family of PU resins is very complex because of the enormous variation in the compositional features of the polyols and isocyanates. This variety results in a large numbers of polymer structures and performance profiles. Indeed, PUs can be rigid solids, soft and elastomeric, or have a foam (cellular) structure.
The majority of PU resins are thermoset. However, there are also important thermoplastic polyurethane resins (TPU). TPUs are elastomers that are fully thermoplastic. Like an thermoplastic elastomers, TPUs are elastomeric and melt-processable. The generally recognized useful features of TPU include high impact strength, even at low temperatures, high elongations, good abrasion resistance, excellent heat resistance, excellent resistance to non-polar solvents, fuels, oils, resistance to ozone, oxidation, and humidity, good electric properties. However, TPUs are also generally characterized by some undesirable performance characteristics, such as high moisture absorption, low strength, and high combustibility.
As a result, a need remains for TPUs that are less susceptible to moisture absorption, have increased strength while maintaining high elongations enhanced resistance to burning, as well as increased heat resistance at elevated temperature.